[clang] [Serialization] Load Specializations Lazily (1/2) (PR #76774)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

> This is a great way to start a new year ;)
> 
> The phab link is https://reviews.llvm.org/D41416.
> 
> In general I was wondering could we simplify the implementation by loading the specialization hash table upon module load. That should be relatively cheap as we will read 2 integers per specialization.
> 
> Perhaps we should put both patches together and that'd allow us to test them if they are on par with https://reviews.llvm.org/D41416 which we use downstream.
> 
> Thanks for working on this!

Hi Vassilev, for testing purpose I sent https://github.com/ChuanqiXu9/llvm-project/tree/LoadSpecializationUpdatesLazily. I didn't create stacked review since I feel a standalone branch may be sufficient.

> In general I was wondering could we simplify the implementation by loading the specialization hash table upon module load. That should be relatively cheap as we will read 2 integers per specialization.

IIUC, it looks like what I do in https://github.com/ChuanqiXu9/llvm-project/commit/7f027f0b6551a8e421034e96bd0a4c953c473df6#diff-c61a3cce4bfa099b5af032fa83cbf1563f0af4bf58dc112b39571d74b6b681c1R3487-R3499. But I don't want to do that with this patch. Since we can avoid load the hash table if the template decl is not loaded.

https://github.com/llvm/llvm-project/pull/76774